A. Field of the Invention
The present invention relates to a solar control film comprised of several layers including a scratch resistant layer containing dispersed carbon black particles. The present invention further relates to a process for preparing the solar control film using a resin composition containing dispersed pigment particles to form the scratch resistant layer.
B. Description of the Related Art
In order to reduce the transmittance of infrared, visible and ultraviolet radiation through the window of a building or vehicle, the art has developed a variety of different products which can be adhered to planar or curved windows. The products, often referred to as solar control films or sheets, alter the solar energy transmission, reflection, and absorption of the window. The most common function is to reduce solar heat gain thereby improving comfort and reducing cooling load within an architectural structure or a vehicle. Some solar control films or sheets are designed so that the surface of the sheet facing away from the rigid window to which the sheet is attached has high thermal infrared reflectivity. Such low emissivity sheets reduce thermal energy loss through glazing and contribute to reduction of heating energy requirements when outdoor temperatures are below indoor temperatures in a building or vehicle.
Solar control sheets may be categorized into three basic types. The simplest sheets reduce light transmission evenly in the visible and infrared wavelengths. These sheets are not considered spectrally selective, and usually contain one thin film layer consisting of an optically neutral nickel alloy. The second type of solar control sheet uses an infrared reflecting metal such as aluminum, copper or silver as a thin film layer and the reflection level in the infrared wavelengths is increased in these sheets making them somewhat spectrally selective. The third type of solar control sheet also contains infrared reflecting metals, but makes use of thin optical interference layers as well.
An illustrative solar control window film consists of a substantially transparent flexible polymer substrate having a thin layer of reflective metal deposited thereon, for example, by vapor deposition or sputter deposition. The film is customarily affixed to the interior surface of a window by a substantially transparent layer of pressure sensitive adhesive. The adhesive customarily contains ultraviolet energy absorbers to protect the contents of the room or space from ultraviolet damage.
Depending upon the selection of the metal or metals and the thickness of the metal layer, the film will have a selected visible light transmission (VLT) and a selected visual light reflection (VLR). In general, VLT and VLR are inversely proportional. If the thickness of the metal layer is increased, VLR is increased and VLT is decreased. In order to achieve an acceptable level of solar energy rejection in most climates, the metal layer must be sufficiently thick and dense that visible light transmission is below 50%, frequently 25% or less. Thus, VLT and VLR become competing interests without a middle of the road compromise acceptable to the industry.
One attempt to increase the VLT of metal films has been to apply coatings of titanium oxide or indium tin oxide adjacent the film or layer of metal to control reflection within a narrow spectral band. According to the principles of optics, sandwiching of the metal film between layers of a material of high refractive index can boost visible transmission, that is, so-called induced transmission. This typically requires 70 to 100 nanometer thick layers of titanium oxide or indium tin oxide, which are very slow to produce and difficult to control. As a result, this approach is generally too expensive to be practical for many window film applications.
U.S. Pat. No. 4,799,745 discloses an infrared reflecting film employing Fabry-Perot interference filters comprised of five or more odd numbers of alternating layers of dielectric and metal. For instance, two or more optically transparent layers of metal, such as silver, gold, platinum, palladium, aluminum, copper, nickel and alloys thereof, are sandwiched between and separated by directly contiguous dielectric spacer layers, which may be oxides of indium, tin, titanium, silicon, chromium and bismuth. U.S. Pat. No. 5,071,206, which issued on a continuation in part of U.S. Pat. No. 4,799,745, discloses a color corrected infrared reflecting film comprised of a substrate bearing seven directly contiguous alternating layers of dielectric and silver. While these films provide the desired visible light transmission, they require 5, 7 or a greater odd number of layers of material sputter deposited onto one another, which is very costly and not easy to achieve.
U.S. Pat. Nos. 4,799,745 and 5,071,206 seek to maximize infrared reflection which, when the film is affixed to a window or employed in a glazing system, causes the reflected infrared energy to be absorbed in the window. Excessive absorption of solar heat can result in breakage of the window. Another disadvantage of this approach is the inherently low moisture vapor transmission rate (MVTR) of the metal/dielectric stack, which typically results in excessively long drying times for the pressure sensitive adhesive attachment or installation system employed to affix the film to a window. In many cases, this can result in fogginess or haze which can disrupt window aesthetics after installation.
U.S. Pat. No. 5,956,175 describes a further arrangement for inhibiting infrared transmission. One disclosed structure includes a substrate having a layer of metal on one side thereof which is adhesively laminated to a clear polymer sheet so that the sheet overlies and protects the metal layer. The exposed surface of the polymer sheet bears a scratch resistance protective hard coat and the exposed other side of the substrate bears a pressure sensitive adhesive for affixing the substrate to a window. In this structure, the near infrared energy absorbing material may optionally be incorporated in the pressure sensitive adhesive, incorporated in or coated onto the substrate, dispersed in the laminating adhesive, incorporated in or coated onto the polymer sheet, dispersed in the hard coat material and/or applied to the substrate as a prime coat under the metal layer and/or to the polymer sheet as a prime coat under the hard coat.
Another approach to selective filtering of the solar spectrum has been through the use of near infrared absorbing dyes. One example is a film incorporating or coated with infrared absorbing dyes that are available from commercial sources, such as Nippon Kayaku Kabushiki Kaisha of Japan. One potential drawback of dyes is that they tend to fade over time. Glass manufacturers have also employed inorganic oxides to absorb solar heat. Examples include PPG Industries “Azurelite” glass and Libby Owens Ford “Evergreen” glass. Again, due to solar heat absorption, very high glazing temperatures are reached, promoting glass breakage, decreasing dual pane insulated glass lifetime, causing sealant failure, and producing an overall inefficient system.
U.S. Pat. No. 5,925,453 describes a window film that is particularly designed for curved glass windows and which minimizes the reflection of infrared rays and reduces the intensity of condensed infrared rays. The window film comprises a light reflecting layer and an infrared absorbing layer with the light reflecting layer inside and the infrared absorbing layer outside. The infrared absorbing layer has a visible light transmittance of 50 percent or more, preferably 60 percent or more. The infrared absorbing agent in the layer can be an organic material, exemplified by phthalocyanines, naphthalocyanines and anthraquinones, or an inorganic material, exemplified by various metal oxides having a particles size in the range of between about 0.005 and about 1 micrometer. The window film is applied to the window via an adhesive layer.
U.S. Pat. No. 5,683,805 describes a colored film formed of a transparent film and at least one colored adhesive layer arranged on one side of the transparent film. The adhesive layer has been colored by a colorant composed of a pigment and a dispersant. The dispersant comprises a (meth)acrylate ester polymer formed, as essential monomer components, of an aromatic vinyl monomer, a primary to tertiary amino-containing (meth)acrylate ester monomer and a (meth)acrylate ester monomer containing an ammonium group quaternized with an aromatic compound. The colorant can be an organic pigment (dye) or an inorganic pigment exemplified by carbon black, metal oxides and metal powders. The separate preparation of the dispersant including the equipment necessary for its preparation constitute significant disadvantages.
U.S. Pat. No. 4,634,637 discloses a solar control film in the form of a composite sheet for use on the inside surface of a motor vehicle window. The composite sheet comprises a first optically clear polymeric stratum having a layer of an alloy of nickel and chromium applied by conventional vacuum deposition to one of its surfaces and having a stripe of stainless steel applied by conventional vacuum deposition over the nickel-chromium layer to one edge of the first polymeric stratum, the nickel chromium alloy layer having a density great enough to reduce the visible light transmission value to about 50–70% and the stainless steel stripe having a density great enough to give a combined visible light transmission with the nickel chromium layer of about 21%. The composite sheet has a second optically clear polymeric stratum having a stripe of an alloy of nickel and chromium applied by conventional vacuum deposition along one side to one edge of the second stratum and having a density great enough to reduce the visible light transmission value through the striped portion to about 35%. The first polymeric stratum is bonded to the second polymeric stratum with the stripe of stainless steel and the stripe of nickel chromium alloy next to and facing each other, the light transmission value of the stainless steel nickel chromium stripe with the nickel chromium layer being about 8 to 12%, the bonding comprising an optically clear adhesive. The sheet further has an optically clear adhesive layer for mounting the composite sheet with the second polymeric stratum to the inside surface of a motor vehicle window.